Dusting of surfaces



1967 K. HUMPHREY ETAL 3,359,128

DUSTING 0F SURFACES Filed June 10, 1965 2 Sheets-Sheet 1 INVENTORS.Loren K. Hum hrey Robert 4. Dunn/n9 iv CUrf/s A. ogmafl Dec. 19, 1967 K.HUMPHREY ETAL 3,359,128

DUSTING 0F SURFACES Filed June 10, 1963 2 Sheets-Sheet 2 INVENTORS.

tare/7 K. Humphrey XWJJ United States Patent 3,359,128 DUSTING 0FSURFACES Loren K. Humphrey, Alma, and Robert A. Dunning and Lurtis A.Layman, Midland, Mich, assignors to The Dow Chemical Qompany, Midland,MiclL, a corporation of Delaware Filed June 10, 1963, Ser. No. 286,672 3Claims. (Cl. 117--16) This invention relates to a method and apparatusfor supplying a uniform coating of a powdered material to the surface ofplastic films or other sheets, especially to reduce the electrostaticcling and tendency to block which is characteristic of many such sheets.

It is well known that any type of sheet materials, especially thosecomprising synthetic plastics, are highly dielectric and that suchsheets have a normal tendency to cling to other sheets which aresimilar. It is also known that this clinging tendency is aggravated byaccumulation of an electrostatic charge thereon, as may be encounteredduring extrusion of the sheet and in such subsequent operations aswinding into or out of storage rolls, or in other manipulations whereinthe sheet surface is subjected to friction.

It is a conventional and normal practice to apply an anti-sticking agentto the surfaces of many sheet materials to reduce their clingingtendency. Numerous powders or dusts have been proposed and are used forsuch purposes. The choice in any given instance depends largely on theintended use of the treated sheet. Plastic films intended for use asfood wrappers are commonly dusted with starch. Sheets intended forindustrial or non-food uses are often dusted with such other agents astalc, mica, various polymer powders and assorted chemicals that haveanti-static properties. Such powders have been applied to the surface ofthe dielectric sheet by such means as sifting or aspirating the powderfrom a continuously diminishing supply. These methods necessarily resultin the deposition of varying doses of the powder per unit area of thesheet surface. Consequently, the extent to which the clinging tendencyis overcome has varied according to the amount of powder remaining inthe duster at the moment each area is treated.

As is apparent, more uniform and controllable results would be desirableto attain in such dusting operation. Such dusts should be uniformlydistributed across the surface of the film.

Many of these devices of the prior art which have been designed todistribute powder uniformly on surfaces have had many shortcomings. Forexample, most devices are relatively complicated and require a largenumber of parts of relatively high precision. Many devices apply thedust to a film in a position remote from the mill roll onto which thesheet or web is being wound, thus providing ample opportunity forelectrostatic forces, drafts, and the like to cause uneven distributionof the dust on the surface thereof.

It is an object of this invention toprovide an improved method andapparatus for the application of dust to a web.

It is a further object of this invention to provide a simple apparatusfor the application of dust to a web.

It is a further object of this invention to provide a method of applyingdust to a web as it is wound onto a roll.

It is a still further object of this invention to provide a method andapparatus for applying dust to a web in an economical manner.

These and other advantageous results, purposes and benefits are achievedin accordance with the method of the invention by utilizing a dustsource directed toward the surface of a web as it is being wound ontoa'roll in such a manner that dust is applied in a gaseous dispersion tothe surface of the roll and the web just prior to the contact onmaintaining said dust source at about the same distance from the rollduring the dusting operation. The apparatus of the invention comprises arewinding stand, said rewinding stand being provided With means tosupport a roll of a web, a dusting chamber adapted to deliver agenerally planiforrn stream of dust dispersed in a gas, said planiformstream directed generally toward the point of contact of the web withthe roll at a location between the roll surface and the surface of theweb about to contact the roll and means to maintain the dusting chamberin spaced relationship from said point of contact.

Further features and advantages of the invention will be more apparentfrom the following description and specification taken in connectionwith the accompanying drawing wherein:

FIGURE 1 is a schematic partly-in-section side view of a dustingapparatus in accordance with the invention;

FIGURES 2 and 3 are views of the dusting chamber utilized in FIGURE 1,and

FIGURE 4 depicts an alternate manner of positioning the dusting chamberwith respect to the roll.

In FIGURE 1 there is delineated a partly-in-section schematicrepresentation of a dusting apparatus generally designated by thereference numeral 10. The apparatus 10 comprises a base member 11carrying an unwind stand 12 which in turn supports a mill roll 13.Adjacent to the unwind stand 12 is a roll support 15 supported from thebase 11 by the pivot 16. The roll support 15 carries a snubber roll 17remotely positioned from the pivot roll 16 and secured in generallyparallel relationship to the mill roll 13. Generally adjacent to thesnubber roll 17 is an idler roll 19. Adjacent the idler roll 19 andremote from the snubber roll 17 is a dancer roll 21. Generally adjacentto the dancer roll 21 and remote from the idler roll 19 is a secondidler roll 22. Generally adjacent the idler roll 22 is a movable idlerroll 24. The movable idler roll 24 is supported by the roll support arms26 which are pivotally afiixed to the base member 11 by means of thepivot 28. The roll supports 15 and 26 are joined by means of arms 29which are aflixed to the roll support 15 at the pivot 30 and to the rollsupport 26 by the pivot 32. A dusting chamber 35 is adjustably afiixedto the roll support 26. The chamber 35 is provided with conduits 36. Theconduits 36 are in full communication with a flexible conduit 38 whichin turn receives a dust air dispersion from the mixing device 40. Themixing device 40 comprises a trough having a hollow body 42 and anupwardly facing opening 43. The body 42 has a gas inlet 45 whichterminates in a nozzle 46. The nozzle 46 is spaced from and is generallycoaxial with an outlet 48 to which is secured the conduit 38. Avibratory feeder 50 provides a continuous supply of undispersed dust 51to the mixing device 40. Positioned generally adjacent to the rollsupport 26 is a rewind stand 54. The rewind stand 54 carries a roll 55formed from a web 55a which is Withdrawn from the mill roll 13, passedunder roll 17, over roll 19, under roll 21, over roll 22 and under roll24 and onto the surface of roll 55.

In FIGURES 2 and 3 there is represented a side and end View of thedusting chamber 35. The dusting chamber 35 comprises a body portion 54partially defining a generally cylindrical space 56. The body 54 alsodefines a tampering slot-like orifice 57 for the discharge of the dustdispersion. The terminal portions of the cavity 56 are closed by the endplates 59 and 59a. A plurality of spaced conduits 36 penetrate the body54 and discharge into the cavity 56 generally along the axis of theconduits 36.

FIGURE 4 depicts an alternate follower arrangement generally designatedby the reference numeral 60. This embodiment of the invention comprisesa dusting chamber carrier 61 supporting a movable idler roll 62. Thecarrier 61 also supports a dusting chamber 64 which delivers a generallyplaniform stream of dust. The carrier 61 is supported by a pair of bellcranks 67 and 68. The bell crank 67 is pivotally attached to the carrier61 by the pivot 70 while the bell crank 68 is pivotally attached to thecarrier 61 by the pivot 71. The bell cranks 67 and 68 are rotatablysupported by a frame 69 at the pivot points 73 and 74. The arm of thebell crank 67 opposite the pivot point 70 is pivotally attached to afollower arm 75 and a connecting link 76 by means of the pivot 78. Theconnecting arm 76 is connected to the bell crank 68 by means of thepivot 79. The follower arm 75 is connected to the pivot 78 of the bellcrank 67, passes through a guide 80 which is fixed relative to the pivotpoints 73 and 74. A follower roll 81 is carried by the end of thefollower arm 75 remote from the pivot 78. The follower roll 81 isadapted to engage a mill roll 84 upon which is being wound a web 85. Theplaniform dust dispersion 65 is directed toward the point of contactbetween the web 85 and the roll 84.

The apparatus of FIGURE 1 in normal operation feeds the web 55a from themill roll 13 underneath the follower roll 17 over the idler roll 19under the dancer roll 21, which serves to maintain constant tension onthe web between the mill roll 13 and the mill roll 55. The idler roll 22serves to guide the web beneath the movable idler 24 and maintain adesired point of contact between the web 55a and the roll 55. As themill roll 13 is reduced in diameter the mill roll 55 increases indiameter. The follower roll 17 contacts the periphery of mill roll 13and moves toward its axis of rotation. Thus the roll support causes theconnecting arm 29 to move toward the unwind stand 12 thus withdrawingthe dusting chamber 35 from the center of rotation of the mill roll 55as its diameter increases. The dusting chamber 35 provides for agenerally circular path of the dust dispersion within the containerprior to being ejected from the slot 57. The configuration of the inletconduits 36 to the chamber 35 effectively prevents dust from beingretained within the chamber 35 due to the generally tangential entry ofthe air. Beneficially a dust mixture may be supplied to the dustingapparatus in accordance with the invention by means of an air conveyersubstantially as shown in FIGURE 1. The trough or container 42 is filledwith the dust to be dispersed. A gas such as air issuing from the nozzle46 tends to entrain the surrounding dust and force it into the conduit48. Effectively the arrangement of the nozzle and the conduit comprisesa venturi system and is eminently successful in providing dispersions offinely divided particles in a gas such as a dispersion of finelypowdered starch in air. Advantageously a vibratory feeder may beutilized to maintain a convenient level of the undispersed dust in thedispersing unit 40. The embodiment illustrated in FIGURE 1 is eminentlysuitable for most dusting applications wherein the variation in diameterof a roll being rewound is not greater than about 4:1. That is, themaximum diameter of the roll is about 4 times the diameter of the corefrom which the film is being rewound or the undusted roll is not reducedto a diameter less than A of its original diameter. As is obvious thedisplacement of the dusting chamber 35 is not directly in relation tothe increase in diameter of the mill roll 55. However, for many dustingoperations this arrangement is eminently satisfactory.

When extremely large rolls wound on small cores are utilized, theembodiment of FIGURE 4 is particularly advantageous. In operation of theembodiment of FIG- URE 4 the dusting chamber 64 and the idlerroll 62 aresupported on the carrier 61. The carrier 61 in turn is movably supportedat the pivot points 70 and 71 by the bell cranks 67 and 68 respectively.As the mill roll 84 increases in diameter the follower roll 81positioned against the outer undusted surface of the film is forcedthrough the guide rotating the bell crank 67 about its pivot point 73;however, the connecting arm 76 alters the bell crank 68 about its pivotpoint 74 in a manner similar to the positioning of the bell crank 67.Thus the dusting chamber is positioned relative to the contact point ofthe web and the roll 84 in a manner which is substantially proportionalto the diameter of the mill roll 84.

By way of further illustration, the dusting apparatus has been employedsuccessfully with very satisfactory results for applying starch dusts tonormally crystalline vinylidene chloride polymer films varying inthickness from one-half to 3 mils at rates of between 3 to 500 feet perminute. No significant operation difiiculties have been encountered whendry dispersible dusts are employed. However, when dust carryingappreciable quantities of water or when dusts are dispersed with air inwhich water was entrained, tendencies to plug may be encountered.

Under normal operating conditions, the apparatus runs continuously forextended periods of several months and longer, continuously providing auniform coating of dust to the surface of the dielectric film andremoving and cleaning the dust laden air without contamination ofadjacent areas. Tendency to give dust patterns or streaks or non-uniformapplication, as is plainly evident in the conventional types ofapparatus that are usually employed for such operation, is absent forall practical purposes when the apparatus of this invention is used.

The apparatus of the invention has been illustrated and described in itsmost simple form. It should be understood that more elegant positioningdevices may be utilized, for example, the follower roll 81 is readilyreplaced with an optical sensing device or even an ultrasonic sensingdevice in order to avoid any contact with the surface of the roll andpushing of the carrier 61 is then readily accomplished by means ofsuitable servo mechanisms well known to the art. Conveniently a sensingelement such as an ultrasonic detector or optical detector inconjunction with a null-balance bridge is suitably used to control theservo mechanism. However, for the majority of applications such elegantinstrumentation is not necessary. Extended operation of dustersfabricated substantially as shown in lFIGURES 1-3 of the presentapplication indicate that dispersion of dust is very uniform, control isprecise, and changes in the dust coating with changes in humidity ofroom air are very small and are generally insignificant. Also filmshaving varying electrostatic charges on their surfaces are dusteduniformly. One significant advantage of the present invention is thelack of stray dust and loss of dust to the surrounding atmosphere. Asthe dust is, blown through the windup net, it appears to be retained bythe film rather than losing a majority portion of the dust to thesurrounding atmosphere.

As is apparent from the foregoing specification, the apparatus andmethod of the present invention are susceptible of being embodied withvarious alterations and modifications which may differ particularly fromthose that have been described in the preceding specification anddescription. For this reason, it is to be fully understood that all ofthe foregoing is intended to be merely illustrative and is not to beconstrued or interpreted as being restrictive or otherwise limiting ofthe present invention, excepting as it is set forth and defined in thehereto appended claims.

What is claimed is:

1. A method of dusting the surface of a web comprising directing agaseous dispersion of the dust in the form of a generally planiformblast on to the surface of a web as it is being wound onto a roll theplaniform blast being directed toward the point of contact of the websurface with the roll and maintaining the supply of said dust at about aconstant rate for the entire winding operation.

2. A method of claim 1 wherein a source of dust dis- 2,057,548 10/1936Wallach et a1. 117--16 persion is maintained at substantially a constantdistance 2,163,642 6/1939 Waliaeh 11716 from the point of contact of theweb with the roll. 2,936,473 5/1961 Ritzerfeld t a1, 117- 16 3. Themethod of claim 1 wherein the dust dispersion ,035 5 4 19 4 sheeban 1171 is a dispersion of dust in air and the web is a therm pl 5 3,163,55312/1964 Commanday et a1. 7 tic web.

References sited WILLIAM D. MARTIN, Primary Examiner. UNITED STATESPATENTS A. H. ROSENSTEIN, P. F. ATTAQUILE, 1,008,993 11/1911 Seward242--83 Assistant Examiners.

1,745,644 2/1930 Royle 242-82 10

1. A METHOD OF DUSING THE SURFACE OF A WEB COMPRISING DIRECTING AGASEOUS DISPERSION OF THE DUST IN THE FORM OF A GENERALLY PLANIFORMBLAST ON TO THE SURFACE OF A WEB AS IT IS BEING WOUND ONTO A ROLL THEPLANIFORM BLAST BEING DIRECTED TOWARD THE POINT OF CONTACT OF THE WEBSURFACE WITH THE ROLL AND MAINTAINING THE SUPPLY OF SAID DUST AT ABOUT ACONSTANT RATE FOR THE ENTIRE WINDING OPERATION.